[tip: x86/urgent] x86/e820: Don't reserve SETUP_RNG_SEED in e820

[tip-bot2 for Jiri Bohac]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     7fd817c906503b6813ea3b41f5fdf4192449a707
Gitweb:        https://git.kernel.org/tip/7fd817c906503b6813ea3b41f5fdf4192449a707
Author:        Jiri Bohac <jbohac@xxxxxxx>
AuthorDate:    Wed, 31 Jan 2024 01:04:28 +01:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Fri, 01 Mar 2024 10:27:20 -08:00

x86/e820: Don't reserve SETUP_RNG_SEED in e820

SETUP_RNG_SEED in setup_data is supplied by kexec and should
not be reserved in the e820 map.

Doing so reserves 16 bytes of RAM when booting with kexec.
(16 bytes because data->len is zeroed by parse_setup_data so only
sizeof(setup_data) is reserved.)

When kexec is used repeatedly, each boot adds two entries in the
kexec-provided e820 map as the 16-byte range splits a larger
range of usable memory. Eventually all of the 128 available entries
get used up. The next split will result in losing usable memory
as the new entries cannot be added to the e820 map.

Fixes: 68b8e9713c8e ("x86/setup: Use rng seeds from setup_data")
Signed-off-by: Jiri Bohac <jbohac@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Link: https://lore.kernel.org/r/ZbmOjKnARGiaYBd5@xxxxxxxxxxxxx
---
 arch/x86/kernel/e820.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index fb8cf95..b66f540 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1017,10 +1017,12 @@ void __init e820__reserve_setup_data(void)
 		e820__range_update(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
 
 		/*
-		 * SETUP_EFI and SETUP_IMA are supplied by kexec and do not need
-		 * to be reserved.
+		 * SETUP_EFI, SETUP_IMA and SETUP_RNG_SEED are supplied by
+		 * kexec and do not need to be reserved.
 		 */
-		if (data->type != SETUP_EFI && data->type != SETUP_IMA)
+		if (data->type != SETUP_EFI &&
+		    data->type != SETUP_IMA &&
+		    data->type != SETUP_RNG_SEED)
 			e820__range_update_kexec(pa_data,
 						 sizeof(*data) + data->len,
 						 E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);